1. Field of the Invention
This invention relates to ballistic resistant articles having excellent resistance to deterioration due to liquid exposure. More particularly, the invention pertains to ballistic resistant fabrics and articles that retain their superior ballistic resistance performance after exposure to liquids such as seawater and organic solvents, such as gasoline and other petroleum-based products.
2. Description of the Related Art
Ballistic resistant articles containing high strength fibers that have excellent properties against projectiles are well known. Articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from fabrics comprising high strength fibers. High strength fibers conventionally used include polyethylene fibers, aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, glass fibers and the like. For many applications, such as vests or parts of vests, the fibers may be used in a woven or knitted fabric. For other applications, the fibers may be encapsulated or embedded in a polymeric matrix material to form woven or non-woven rigid or flexible fabrics. Preferably each of the individual fibers forming the fabrics of the invention are substantially coated or encapsulated by the binder (matrix) material.
Various ballistic resistant constructions are known that are useful for the formation of hard or soft armor articles such as helmets, panels and vests. For example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are incorporated herein by reference, describe ballistic resistant composites which include high strength fibers made from materials such as extended chain ultra-high molecular weight polyethylene. These composites display varying degrees of resistance to penetration by high-speed impact from projectiles such as bullets, shells, shrapnel and the like.
For example, U.S. Pat. Nos. 4,623,574 and 4,748,064 disclose simple composite structures comprising high strength fibers embedded in an elastomeric matrix. U.S. Pat. No. 4,650,710 discloses a flexible article of manufacture comprising a plurality of flexible layers comprised of high strength, extended chain polyolefin (ECP) fibers. The fibers of the network are coated with a low modulus elastomeric material. U.S. Pat. Nos. 5,552,208 and 5,587,230 disclose an article and method for making an article comprising at least one network of high strength fibers and a matrix composition that includes a vinyl ester and diallyl phthalate. U.S. Pat. No. 6,642,159 discloses an impact resistant rigid composite having a plurality of fibrous layers which comprise a network of filaments disposed in a matrix, with elastomeric layers there between. The composite is bonded to a hard plate to increase protection against armor piercing projectiles.
Hard or rigid body armor provides good ballistic resistance, but can be very stiff and bulky. Accordingly, body armor garments, such as ballistic resistant vests, are preferably formed from flexible or soft armor materials. However, while such flexible or soft materials exhibit excellent ballistic resistance properties, they also generally exhibit poor resistance to liquids, including fresh water, seawater and organic solvents, such as petroleum, gasoline, gun lube and other solvents derived from petroleum. This is problematic because the ballistic resistance performance of such materials is generally known to deteriorate when exposed to or submerged in liquids. Further, while it has been known to apply a protective film to a fabric surface to enhance fabric durability and abrasion resistance, as well as water or chemical resistance, these films add weight to the fabric. Accordingly, it would be desirable in the art to provide soft, flexible ballistic resistant materials that perform at acceptable ballistic resistance standards after being contacted with or submerged in a variety of liquids, and also have superior durability without the use of a protective surface film in addition to a polymeric binder coating. The present invention provides a solution to this need.
Few conventional binder materials, commonly referred to in the art as polymeric “matrix” materials, are capable of providing all the desired properties discussed herein. Nitrile rubber polymers are desirable in other arts due to their resistance to dissolution, penetration and/or transpiration by sea water and resistance to dissolution, penetration and/or transpiration by one or more organic solvents, such as diesel gasoline, non-diesel gasoline, gun lube, petroleum and organic solvents derived from petroleum. It has been discovered that nitrile rubber or nitrile rubber-containing coatings advantageously contribute to the retention of the ballistic resistance properties of a ballistic resistant fabric after prolonged exposure to potentially harmful liquids, eliminating the need for a protective surface film to achieve such benefits, while maintaining good flexibility. Excellent ballistic and environmental properties have also been achieved when coating ballistic resistant fibrous materials with a composition comprising a blend of a nitrile rubber or nitrile rubber-containing polymer and a fluorine-containing polymer, which includes fluorine-containing oligomers and fluorine-containing resins.